The fluid-structure interaction of bristled wings

Slender structures covered with hairs, bristles, or branches are commonly observed in nature, from plants to marine animals and insects, to crustaceans and other arthropods. The functions of these porous, "hairy" structures are diverse and essential, ranging over feeding, sensing, and locomotion. A particularly intriguing example is the bristled wings of miniature insects, the smallest of which is comparable to a paramecium, a single-cell organism. Compared to the more familiar membrane wings, bristled wings reduce the amount of material in the wing, lowering the load the insects carry in flight. With bristled wings, miniature insects achieve flight via drag-based flght mechanisms. Operating at a low bristle Reynolds number, the seemingly leaky bristled wings act as paddles due to the viscous boundary layers plugging the flow between bristles. Due to their stunning size and geometry, bristled wings have garnered considerable interest in recent years. We tackle several yet-unsolved questions, such as: What is the optimal number of bristles on the wing? What is the most lightweight configuration that can withstand its own drag forces and avoid reconfiguration? To investigate the trade-off among weight, stiffness, and aerodynamic force generation of the bristled wings, we combine experiments and simulations to characterize the drag coefficients of idealized models of bristled wings. Particular emphasis is given to the role of elastic deformation of the bristles in modifying the generated drag.